Combination regimens of RTV and IDV in adults offer the benefit of two potent antiretroviral agents, convenience of twice-daily dosing, unrestricted timing of meals, and fewer renal complications. There are limited, largely anecdotal data from children suggesting that initial virologic response can also be attained in children given IDV with RTV, but there are not sufficient pharmacokinetic data to define appropriate dose regimens. This study will evaluate the clinical feasibility of a combination RTV and IDV regimen for children.